The objective of this research is to investigate the effects of halothane, one of the most commonly employed inhalational anesthetics, on the ultrastructure of mouse neuroblastoma cells, crayfish nerve cords, and cultured human lymphocytes. Particular emphasis will be placed on the effects of halothane on microtubules and microfilaments and the role of these fibrous organelles in the processes of cell division and differentiation, axonal transport, and the phytohemagglutinin-stimulated blastic transformation of lymphocytes. Related experiments will investigate possible distributional rearrangements of specific intracellular enzymes in response to halothane treatment. Other experiments will examine the halothane- induced transformation of crayfish nerve cord microtubules into macrotubular forms, the possibility that halothane can interact directly with isolated microtubules, and attempt to characterize the composition and function of microtubule-associated filamentous complexes in crayfish axons.